Diffusion tensor imaging (DTI) is a variation of magnetic resonance imaging (MRI) and allows the observation of molecular diffusion in tissues in vivo and, therefore, the molecular organization in tissues. Presently, DTI is the only method available to study in vivo and non-invasively the architecture of axonal fibers in the central nervous system.
In DTI, several sets of diffusion weighted images are acquired with the diffusion gradients applied in different directions. This allows quantitative measurements of the anisotropic diffusion of molecules in biological tissue, and this diffusion anisotropy reflects the presence of spatially oriented structures (e.g., the myelinated axonal fibers running in parallel). The molecular mobility in the spatially oriented structures is not likely to be the same in all directions. For instance, diffusion along the fibers is more pronounced than diffusion transverse to the length of the fibers.
DTI measurements involve MRI scans of a target area, e.g., a portion of the brain. As DTI systems are developed, tested and/or placed in operation, their accuracy must be verified (i.e., calibrated) to ensure accurate results and safe operation of the systems. Generally speaking, calibration and/or test measurements are performed using a phantom. As is known in the art, a phantom is any structure that contains one or more tissue substitutes, and generally is used to simulate the human body. A tissue substitute is defined as any material that simulates a body of tissue.
Numerous phantoms have been developed for various imaging techniques. For example, U.S. Pat. No. 6,744,039 relates to a fillable phantom for use with nuclear imaging. More specifically, the phantom includes a container, a porous medium within the container, and a connector for filling the container with a radioactive solution. One or more contrasting regions formed in the porous medium are in fluid communication with the porous medium in order to absorb the radioactive solution. The phantom provides radioactive hot spots within a less radioactive background.
U.S. Pat. No. 6,720,766 relates to a thin film phantom for testing and measuring the performance of magnetic resonance imaging (MRI) and x-ray computed tomography (CT) imaging systems. The phantom includes a planar medium and a plurality of individually sub-resolvable scatters having preselected magnetic resonance properties within a pattern of resolvable regions on the surface of the medium. The phantom can be used to check the quality of images obtained from the MRI and CT systems.
U.S. Pat. No. 6,409,515 describes a phantom for a real-time interactive imaging system. The phantom includes a plurality of segments having unique identifiers, the segments joining together to form a polyhedron around an inner plate. In one embodiment, the inner plate has a unique identifier and two inner blocks positioned orthogonally upon it, each inner block also having a unique identifier. The phantom provides a variety of uniquely identified surfaces, angles and edges for scanning practice in a real-time interactive environment, and enables the imaging system user to verify image correctness and annotation.